Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.76   10.851%   $224.7615   $224.76   $224.75   $224.80  
  Purchase #2 $227.41   3.317%   $234.9532   $234.95   $234.95   $235.00  
  Purchase #3 $222.94   8.762%   $242.474   $242.47   $242.45   $242.50  
  Purchase #4 $58.65   9.232%   $64.0646   $64.06   $64.05   $64.10  
  Purchase #5 $64.63   13.735%   $73.5069   $73.51   $73.50   $73.50  
  Purchase #6 $171.65   4.362%   $179.1374   $179.14   $179.15   $179.10  
  Purchase #7 $225.78   12.380%   $253.7316   $253.73   $253.75   $253.70  
  7 purchase totals = $1,173.82       $1,272.6292   $1,272.62   $1,272.60   $1,272.70